The proliferation of normal breast tissue implanted into athymic nude mice is stimulated by estrogen, but not by progesterone.

Authors: Laidlaw IJ, Clarke RB, Howell A, Owen AW, Potten CS, Anderson E.

Publication Year: 1995

Citation: Endocrinology 1995;136(1):164-71.

Normal human breast tissue was implanted subcutaneously into athymic nude mice. The mice were then treated with estradiol or progesterone such that serum levels approximated those seen in normal menstruating women. Immunocytochemical measures were made of proliferative activity and steroid receptor expression of the tissue implants. It was found that physiologic levels of estradiol significantly stimulated the proliferation of human breast epithelial cells and increased progesterone receptor expression 10-20-fold. Progesterone failed to affect proliferation alone or after estradiol priming.

http://www.ncbi.nlm.nih.gov/pubmed/7828527